This invention relates to remediation of organic contaminants in gas and/or vapor streams. More particularly, the invention relates to biodegradation of volatile organic compounds in gas and/or vapor streams wherein the volatile organic compounds are sparingly soluble in aqueous solutions. Biodegradation is enhanced by decreasing the distribution coefficient, thus increasing the solubility, of sparingly soluble vapors in aqueous solution with a water soluble, non-toxic, inert polymer.
The remediation of air, soil, and water pollution has become an international priority. Around the globe, countries are instituting laws for protecting and cleaning the environment. Numerous technologies for reducing pollution and cleaning existing polluted sites are already known. One such technology that is gaining favor is bioremediation, i.e. the remediation of pollution by systems containing living organisms. The U.S. government, for example, has taken notice of bioremediation and has become a major source of funding for research and development thereof. In fiscal 1993, the U.S. Environmental Protection Agency budgeted $10 million, the Department of Defense budgeted $11 million, and the Department of Energy budgeted over $30 million for research and development of bioremediation technology. Bioremediation is advantageous when pollutant concentration in the waste gas is low. Moreover, the pollutants are converted to harmless oxidation products, e.g. CO.sub.2 and H.sub.2 O, and the process can be carried out at low temperature and pressure.
Volatile organic compounds (VOCs) are produced by a variety of industries, including the chemical, fossil fuel, mining, manufacturing, agriculture, and food processing industries. Moreover, waste gases are also a product of remediation of soil and groundwater pollution wherein toxic organic vapors are extracted from subsurface soils and water. Such waste gases include, for example, gasoline vapors from vapor vacuum extraction (straight chain alkanes), ethylene from polyethylene manufacturing, and styrene from polystyrene manufacturing. Bioreactors are used to degrade a wide range of VOCs in waste gases. Three conventional bioreactors for treating waste gases are biofilters, trickling filters, and bioscrubbers. In biofilters and trickling filters, the gas passes through a filter bed to which bacteria residing in an aqueous phase are attached. In biofilters, the aqueous phase is stationary, whereas in trickling filters the aqueous phase is mobile. The water-soluble compounds in the gas are transferred to the liquid, from which they diffuse into the biolayer. In bioscrubbers, microorganisms are suspended in a moving aqueous phase. The contaminants are absorbed in a scrubber type of gas/liquid contactor where the culture medium containing the microorganisms is sprayed, and are subsequently degraded in an aerated stirred-tank reactor or "regenerator." These reactors have been used to degrade a wide range of water soluble gases. Degradation of sparingly soluble gases and vapors, however, has met with limited success.
Recently, two-phase systems have been proposed for biodegradation of poorly water soluble VOCs. In these systems, the VOC is transferred to a water-immiscible solvent that has a high affinity for the VOC. The VOC is contacted with the solvent in a gas absorber or trickle bed, and this VOC-rich solvent is then contacted with an aqueous bacterial suspension for degradation. M. T. Cesario et al., Biological Treatment of Waste Gases Containing Poorly-Water-Soluble Pollutants, in Biotechniques for Air Pollution Abatement and Odour Control Policies 135 (A. J. Dragt & J. van Ham eds., 1992); B. De Heyder et al., Biotechnological Removal of Ethene from Waste Gases, in Biotechniques for Air Pollution Abatement and Odour Control Policies 309 (A. J. Dragt & J. van Ham eds., 1992); S. El Alaam et al., High Efficiency Styrene Biodegradation in a Biphasic Organic/Water Continuous Reactor, 39 Appl. Microbiol. Biotechnol. 696 (1993). This method does not increase substrate availability in the aqueous phase and still requires transfer from the organic phase to the aqueous phase for degradation to occur.
Surfactants have been used to enhance the solubilization of long chain hydrocarbons and polycyclic aromatic hydrocarbons. S. J. Bury & C. A. Miller, Effect of Micellar Solubilization on Biodegradation Rates of Hydrocarbons, 27 Environ. Sci. Technol. 104 (1993), reported that the specific growth rate of certain bacterial strains and the degradation rates of n-decane can be significantly increased if straight-chain ethoxylated alcohols that are nonionic, nontoxic, readily biodegradable, and have very low critical micelle concentrations (CMCs) are added to the aqueous phase. A. Tiehm, Degradation of Polycyclic Aromatic Hydrocarbons in the Presence of Synthetic Surfactants, 60 Appl. Environ. Microbiol. 258 (1994), reported similar results for polycyclic aromatic hydrocarbons using polyethoxylated alcohols and polyethoxylated alkylphenol surfactants. These articles described use of surfactants to degrade liquid or solid phase pollutants, such as would be encountered in soil bioremediation. See also A. Oberbremer et al., Effect of the Addition of Microbial Surfactants on Hydrocarbon Degradation in a Soil Population in a Stirred Reactor, 32 Appl. Microbiol. Biotechnol. 485 (1990); W. F. Guerin & G. E. Jones, Mineralization of Phenanthrene by a Mycobacterium sp., 54 Appl. Environ. Microbiol. 937 (1988); D. E. Kile & C. T. Chiou, Water Solubility Enhancements of DDT and Trichlorobenzene by Some Surfactants Below and Above the Critical Micelle Concentration, 23 Environ. Sci. Technol. 832 (1989); K. D. Pennell et al., Surfactant-Enhanced Solubilization of Residual Dodecane in Soil Columns, 27 Environ. Sci Technol. 2332 (1993).
Surfactants have also been used to enhance the solubility of certain gases. A. D. King, Jr., Solubilization of Gases by Polyethoxylated Nonyl Phenols, 137 J. Colloid Interface Sci. 577 (1990), and A. D. King, Jr., Solubilization of Gases by Polyethoxylated Lauryl Alcohols, 148 J. Colloid Interface Sci. 142 (1992), disclosed that solubilities of oxygen, argon, methane, ethane, and propane in aqueous solutions of polyethoxylated nonyl phenols and polyethoxylated lauryl alcohols increase with surfactant concentration, as expected with micellar solubilization. The intramicellar solubility of each gas decreases as the mole ratio of ethylene oxide to nonyl phenol or mole ratio of ethylene oxide to lauryl alcohol increases. These results indicate that polymerized ethylene oxide groups do not contribute to the solubilization of these gases. Instead, the solubilizing capacities of the hydrophobic interiors of these micelles are found to closely approximate the bulk solubility of nonyl phenol or lauryl alcohol.
In view of the foregoing, it will be appreciated that a method of increasing biodegradation of sparingly soluble volatile organic compounds that contaminate gas streams or vapors would be a significant advancement in the art.